In recent years, piezoelectric vibrators having piezoelectric vibrating reed using crystals or the like have been used in mobile phones or personal digital assistants, as a time source or a timing source of a control signal, a reference signal source and the like.
In the piezoelectric vibrator, miniaturization is further desired due to the miniaturization of equipment to be mounted thereon. As a method of promoting miniaturization, several methods have been considered, but as one of them, there is a method of using a tuning fork type of piezoelectric vibrating reed in which a groove portion is formed on both surfaces of a vibration arm portion.
Usually, the tuning fork type of piezoelectric vibrating reed has a pair of vibration arm portions which is arranged in parallel to each other and has the proximal end side integrally fixed to a base portion, and an excitation electrode that is formed on the outer surfaces (including a grove portion) of the pair of vibration arm portions and vibrates the pair of vibration arm portions.
The excitation electrode is an electrode which vibrates the pair of vibration arm portions in a direction approaching and retreating from each other at a predetermined resonance frequency, and is electrically connected to a mount electrode formed on the outer surface of the base portion via a lead-out electrode. Moreover, the voltage is applied the piezoelectric vibrating reed via the mount electrode.
Herein, in a case where the groove portion is formed in the pair of vibration arm portions, as shown in FIG. 27, two excitation electrodes 93 and 94 with different polarities are formed on the side surfaces of the vibration arm portions 90 and 91 and on the side surface of the groove portion 92. At this time, since two excitation electrodes 93 and 94 are in an opposed positional relationship, as compared to a case where the groove portion 92 is not formed, an electric field is more effectively apt to act. For that reason, even when the size of the piezoelectric vibrating reed 95 is miniaturized, the vibration loss is low and a CI (equivalent resistance value) can be actively suppressed. Thus, there is an advantage in that it is suitable for miniaturization.
However, the piezoelectric vibrating reed 95 is generally manufactured by etching a wafer substrate such as a crystal (e.g., see Patent Citation 1). Moreover, in a case where the piezoelectric vibrating reed 95 having the groove portion 92 is manufactured, after the exterior shape of the piezoelectric vibrating reed 95 is formed in an initial etching process, the groove portion 92 is formed in the next etching process. At this time, the process is performed by a wet etching using a liquid agent such as hydrogen fluoride water.    [Patent Citation 1] Japanese Patent No. 3729249
However, in the method of the related art, the following problem remains.
Firstly, the etching process by wet etching has a property of being affected by a surface orientation of crystal of the wafer substrate. For that reason, in the method of the related art in which the process of the exterior shape and the process of the groove portion 92 are performed by wet etching, the side surface or the bottom surface of the etched groove portion 92 does not become the flat surface but becomes a distorted shape as shown in FIG. 28, and an irregularity in the surface occurs. Moreover, since the exterior shape is also processed by wet etching, not only the groove portion 92, but also vibration arm portions 90 and 91 or the side surface of the base portion also do not become the flat surface but become the distorted shape. For that reason, it is impossible to accurately form the groove portion 92 in a desired shape in the piezoelectric vibrating reed 95. Furthermore, an additional etching may be necessary depending on the extent of the irregularity in the surface.
Moreover, when the shape of the groove portion 92 forms the excitation electrodes 93 and 94 in the state as shown in FIG. 28, the excitation electrodes 93 and 94 are not in a secure opposed positional relationship, with the result that the CI value cannot be set at the designed value. In addition, there is a concern that each electrode may be shortened. Thus, high quality and high performance are difficult to promote.
On the other hand, in a case where the above-mentioned etching is performed not by wet etching but by a dry etching, it is not affected by the surface orientation of crystal, the above-mentioned problem does not occur. However, when dry etching is adopted, the following problem occurs.
When performing dry etching, generally, after a protective film is formed in an area other than an area where the etching is performed on the wafer substrate surface, the wafer substrate is subjected to dry etching and is processed to a desired shape. Herein, since there is a need to deeply dig the wafer substrate in forming the groove portion 92 in the wafer substrate, a film of a hard metallic element such as Ti, Ni or Cr is adopted as the protective film, and it is necessary to increase the thickness of the protective film. However, since the stress is great on the film of the hard metallic element, when the thickness of the protective film is thickened, there is a problem in that bending of the wafer substrate may occur. That is, there is a concern that it may be impossible to form a desired groove portion 92 even when dry etching is performed in the state in which the wafer is bent.
The present invention was made in view of the above circumstances, and an object thereof is to provide a method of manufacturing a piezoelectric vibrating reed that can form a desired groove portion in a vibration arm portion by dry etching, furthermore, an oscillator, electronic equipment and a radio-controlled timepiece having the piezoelectric vibrator.